Touch panels are widely applied to many electronic products, such as mobile phones, personal digital assistants (PDAs), digital cameras, media players, computers, satellite navigation devices, touch screens, etc. The currently existing touch panels are divided into many types, such as resistive touch panels, capacitive touch panels, optical touch panels, among which the optical touch panels have the lowest cost.
Referring to FIG. 1, there shows a schematic view of an optical touch panel assembly 100. The optical touch panel assembly 100 has a substantially rectangular touch panel 101 and includes three light sensors 110a, 110b, 110c, three light sources 120a, 120b, 120c, and four light reflective bars 130a, 130b, 130c, 130d. The three light sources 120a, 120b, 120c are disposed on the three light sensors 110a, 110b, 110c, respectively, and emit lights toward the touch panel 101. The four light reflective bars 130a, 130b, 130c, 130d are disposed adjacent to four side edges of the touch panel 101, respectively. The three light sensors 110a, 110b, 110c are disposed at three corners of the touch panel 101, respectively, and each light sensor is positioned at a joint of corresponding two adjacent light reflective bars. The light sensors 110a, 110b are respectively positioned at two ends of one diagonal line 102 of the touch panel 101.
Each light sensor is used for sensing the light reflective brightness of a corresponding light reflective bar. For example, the light sensor 110a is used for sensing the light reflective brightness of the light reflective bars 130a, 130b. The light sensor 110a has a plurality of linearly arrayed pixels therein, and each pixel is used for sensing a specific area of the light reflective bar 130a or 130b. When a shade O such as a finger moves or operates within the touch panel 101, some of the pixels of the light sensor 110a are shaded by the shade O, such that the brightness sensed by the some of the pixels of the light sensor 110a is lower than the brightness sensed by the other pixels of the light sensor 110a. Similarly, the other light sensors 110b, 110c also have some pixels are shaded by the shade O, and the brightness sensed by the shaded pixels is lower than the brightness sensed by the other pixels of the light sensors 110b, 110c. The position information of the shade O can be calculated according to the brightness change sensed by the light sensors 110a, 110b, 110c. 
As the light sensors 110a, 110b, 110c are disposed at the corners of the touch panel 101, there always needs to provide a large receiving gap between every two adjacent light reflective bars for receiving a light sensor therein. However, in use, the receiving gaps form dark areas that cannot be sensed by the light sensors. In terms of the light sensor 110a, some pixels of the light sensor 110a face towards the light sensor 110b instead of a light reflective bar. In other words, the some pixels of the light sensor 110a are faced with a dark area formed by the light sensor 110b. Therefore, the brightness sensed by the some pixels of the light sensor 110a is sensibly lower than the brightness sensed by the other pixels of the light sensor 110a. Thus, the light source 120b disposed on the light sensor 110b is provided and used for supplementing light to the light sensor 110a, thereby ensuring the brightness sensed by all of the pixels of the light sensor 110a are uniform when no shade O is present. Therefore, as the light sensor 110a works, the light source 120a operates in a normal light-emitting state, while the light source 120b operates in a supplementary light-emitting state, the brightness of the normal light-emitting state being higher than that of the supplementary light-emitting state. Similarly, when the light sensor 110b works, the light source 120b operates in a normal light-emitting state, while the light source 120a operates in a supplementary light-emitting state.
As the light sources 120a, 120b of the existing optical touch panel assembly 100 each must have two (i.e., normal and supplementary) light-emitting states in operation, a driving circuit of the light sources 120a, 120b becomes complex.
Therefore, there is room for improvement within the art.